1. Field of the Invention
The invention relates to a method and a device for determining the degree of fouling or soiling of a printing unit of a printing machine.
2. Description of the Related Art
In the prior art, rubber blankets, impression cylinders, or the inking units of offset printing machines, for example, have been washed on an empirical basis. In other words, the printing machine operator has to determine the proper timing in the washing cycle, i.e. the point at which the washing cycle should be initiated and the number of spraying runs per washing cycle. Alternatively, washing programs in an automatic control may be set up such that a washing cycle is performed at a fixed point in time depending on the type of machine or the print job. In so doing, there may be cases in which a fixed amount of washing solution is used up, even though much less washing solution would suffice for the washing cycle in many cases. That scenario would also mean a shorter washing cycle, with fewer discrete spraying runs. The rather inaccurate estimates by the operator thus cause an increased use of washing medium. Washing medium may be toxic, explosive or otherwise detrimental to the environment.
German Published, Non-Prosecuted application DE-OS 15 98 831 describes a device for measuring the cloudiness or opacity of a fluid. The device is particularly suited for measuring the degree of opacity of fluids which carry a high concentration of an opaque agent.
Further methods of determining the degree of fouling of an opaque fluid are also conceivable such as, for example, physical, chemical or electrochemical techniques.